# `Bylaw.Db.Adapters.Postgres.Checks.EctoChangesetUniqueConstraints`
[🔗](https://github.com/ryanzidago/bylaw/blob/v0.1.0-alpha.1/lib/bylaw/db/adapters/postgres/checks/ecto_changeset_unique_constraints.ex#L1)

Validates `Ecto.Changeset.unique_constraint/3` annotations for Postgres indexes.

## Examples

With a unique index on `users.email`, before:

```elixir
def changeset(user, attrs) do
  user
  |> Ecto.Changeset.cast(attrs, [:email])
  |> Ecto.Changeset.validate_required([:email])
end
```

The database protects uniqueness, but an insert conflict can bubble up as a
database error instead of a changeset error attached to `:email`.

After, annotate the changeset with the matching constraint:

```elixir
def changeset(user, attrs) do
  user
  |> Ecto.Changeset.cast(attrs, [:email])
  |> Ecto.Changeset.validate_required([:email])
  |> Ecto.Changeset.unique_constraint(:email)
end
```

Ecto can translate the database constraint violation into a normal changeset
error for callers.

## Notes

The check skips dynamic `cast` or `change` field lists, expression indexes,
partial indexes, primary keys, and unique indexes whose columns cannot be
mapped to Ecto schema fields.

## Options

The check discovers compiled Ecto schemas through reflection, parses source
files for conservative changeset candidates, and only requires
`unique_constraint/3` when a candidate casts all fields covered by a unique
Postgres index. Dynamic cast/change field lists are skipped for v1.

Pass `paths: [...]` so Bylaw can parse source AST for user-defined changeset
functions:

```elixir
{Bylaw.Db.Adapters.Postgres.Checks.EctoChangesetUniqueConstraints,
 paths: ["lib/my_app"]}
```

When the repo can report `config()[:otp_app]`, schema module discovery is
derived from it. Use `schema_modules: [...]` when the check should inspect an
explicit set of schemas instead:

```elixir
{Bylaw.Db.Adapters.Postgres.Checks.EctoChangesetUniqueConstraints,
 paths: ["lib/my_app/accounts"],
 schema_modules: [MyApp.Accounts.User, MyApp.Accounts.Organization]}
```

Use `rules: [...]` to scope the Postgres constraints considered by the check:

```elixir
{Bylaw.Db.Adapters.Postgres.Checks.EctoChangesetUniqueConstraints,
 paths: ["lib/my_app"],
 rules: [
   [
     only: [schema: "public"],
     except: [[table: "legacy_users", constraint: "legacy_users_email_index"]]
   ]
 ]}
```

## Usage

Add this module to the checks passed to
`Bylaw.Db.Adapters.Postgres.validate/2`. See the
[README usage section](readme.html#usage) for the full ExUnit setup.

# `check_opt`

```elixir
@type check_opt() ::
  {:validate, boolean()}
  | {:otp_app, atom()}
  | {:paths, [Path.t()]}
  | {:schema_modules, [module()]}
  | {:rules, [keyword()]}
```

# `check_opts`

```elixir
@type check_opts() :: [check_opt()]
```

# `validate`

```elixir
@spec validate(target :: Bylaw.Db.Target.t(), opts :: check_opts()) ::
  Bylaw.Db.Check.result()
```

Implements the `Bylaw.Db.Check` validation callback.

---

*Consult [api-reference.md](api-reference.md) for complete listing*